1. The Field of the Invention
The invention relates to an Internet Protocol (IP) Multimedia Subsystem (IMS) structure hosting at least two different IMS services, wherein at least one of the at least two different IMS services is based on Rich Communications Suite (RCS) for messaging only (RCS-messaging-only) and wherein at least another one of the at least two different IMS services is based on Voice over Long Term Evolution (VoLTE) or Voice over Wireless Fidelity (VoWiFi), respectively VoIP in general.
2. The Relevant Technology
Today mobile phones use the Global System for Mobile Communications (GSM) standard, which belongs to the second-generation of mobile telecommunications technology (2G), as well as the Universal Mobile Telecommunications System (UMTS) standard belonging to the third-generation of mobile telecommunications technology (3G). Further, belonging to the fourth-generation of mobile telecommunications technology (4G), the Long Term Evolution (LTE) standard is an evolution based on GSM and UMTS network technologies and used in the latest generation of mobile phones, smart phones and other user equipment (UE). GSM defines a circuit-switched (CS) network optimized for full duplex voice telephony and data communication (Voice and Circuit Switched Data), wherein so-called Mobile Switching Centers (MSC) switch the connections between the mobile phones and act as interface between the radio network and the fixed line network. In GPRS, i.e. General Packet Radio Service (GPRS) sometimes referred to as 2.5G, data communications are provided by packet data transport. In contrast, UMTS defines a radio access technology using the same core network as GSM/GPRS, but wherein with Release 4 (R4) separate CS control and media layer were introduced with MSC Servers and Media Gateways (MGW). Voice between the MGWs can be transported based on IP. Increased capacity and speed are available in LTE access networks using advanced digital signal processing (DSP) methods wherein the network architecture is fully based on an IP system. The CS core network as such does not exist and voice calls can be handled either by falling back to GSM/UMTS or can be handled by a protocol based on IP, e.g. VoLTE. VoLTE and VoWiFi are fully based on IMS.
For LTE and other IP-based networks the IMS designed by the 3rd Generation Partnership Project (3GPP) provides an architectural frame-work for multimedia services based on packet communication like voice, messaging, etc. (e.g. VoLTE, VoWiFi, VoIP in general, RCS, etc.). Although being originally developed for mobile applications IMS is used in wireless and fixed-line technologies, too. A user, or so-called subscriber, may connect to IMS by registering an IMS terminal directly on an IMS server, wherein the IMS terminal can be a mobile phone including a so-called smart phone, a Personal Digital Assistant (PDA), a computer or any other user equipment (UE). The protocol used in IMS for session handling such as session establishment, modification and termination is the standardized Session Initiation Protocol (SIP).
In IMS different Call Session Control Functions (CSCF) play central roles as they are used to process the SIP signaling packets and manage the IMS sessions. The Proxy CSCF (P-CSCF) is the first contact point for IMS service requests from the SIP clients. It is a SIP proxy and forwards requests from subscribers (SIP user agents) to other CSCFs and vice versa, as described hereafter. Further, the P-CSCF authenticates the subscriber by checking the available authorizations of the subscriber, negotiates the quality of service and may generate data for accounting besides the S-CSCF. The Interrogating CSCF (I-CSCF) requests from the HSS which S-CSCF (see further below) is responsible for managing the desired IMS session for the respective subscriber. The Serving CSCF, S-CSCF, is the main SIP session control node within the overall IMS network. It retrieves user profiles (e.g. the initial Filter Criteria, iFC) from the Home Subscriber Server (HSS) during the registration process, keeps the registration status, forwards the sessions to the different SIP Application Servers (AS) via the iFC and handles the SIP sessions in general. Different services are hosted and executed by different SIP Application Servers (AS) such as Telephony Application Server (TAS) (e.g. VoLTE SIP AS), IM SIP AS and the like. These application servers interface with the S-CSCF. Authentication and authorization of a user is managed by the HSS (as part of the registration process), which is a master user database and contains subscriber profiles. The HSS can provide information about a subscriber's location (S-CSCF), iFC and the like. Different users are discriminated by different identities, typically the Public User Identities (IMPU) and the Private User Identities (IMPI). The IMPU is the identity, which is used by other users to set up a session. In mobile networks this is usually the Mobile Subscriber Integrated Services Digital Network Number (MSISDN). Inter alia there are TEL Uniform Resource Identifiers (TEL URI) each representing a telephone number of one subscriber. Another IMPU, which is used in IMS for internal routing, is the SIP URI representing the corresponding SIP address or addresses of one subscriber, because the IMS uses domain based addressing. The mapping from the TEL URI to the SIP URI is done in the E.164 Number Mapping (ENUM) server. Different networks and subscribers are coupled via Session Border Controllers (SBC). Those SBCs implement sessions for unsecure external data networks in secure internal structures like IMS infrastructures.
Different IMS services can be hosted on the same IMS infrastructures. But for example an IM service can be hosted on one IMS infrastructure, whereas a VoLTE service can be hosted on another IMS infrastructure, too. Due to many different reasons such as centralization etc. and the resulting advantages like reduced maintenance costs for network providers, integration of several IMS services from different infrastructures on one IMS infrastructure is desirable. The present invention relates to a concrete realization of such integration. Hereby, one IMS infrastructure, which may comprise several distributed server machines, hosts different SIP ASs for corresponding IMS services. All these SIP AS's interface with the S-CSCF, which organizes different sessions of different IMS services of corresponding SIP AS's and communicates with the HSS for authorization of users and managing their access to said IMS services.
Certain IMS services may use the Rich Communication Suite (RCS) based on SIP for communication over IMS as RCS offers standardized services for 1-to-1/Group Chat, standalone messaging, file transfer, content sharing, and the like. An IMS infrastructure hosting inter alia an IM service based on RCS, referred to as RCS-message-only in the following, and a VoLTE and/or VoWiFi service may be unable to handle different types of session invitations without failure, as described in the following.
Nowadays, some IMS terminals have certain IMS capabilities like IM but lack other IMS capabilities like VoLTE and/or VoWiFi. For example a mobile User Equipment (UE) may have IM functionality but no VoLTE/VoWiFi functionality (called RCS-messaging-only in the further description). Instead said UE would use 2G/3G CS for telephony. Or a subscriber may have VoLTE/VoWiFi functionality but no access to a LTE or WiFi network.
Lacking functionality for and/or lacking access to a certain IMS service of an UE is referred to as lacking IMS service capability of a subscriber hereafter. Further, a subscriber may have a certain IMS service capability but no allowance to use this IMS service. This is referred to as lacking IMS service authorization of a subscriber subsequently.
In one exemplary scenario a subscriber named B with UE B has IM capability and an associated authorization but no VoLTE and/or VoWiFi capability and/or an associated authorization and uses 2G/3G CS for telephony (RCS-message-only subscriber). Another subscriber A with UE A has both IM and VoLTE capability and authorization. In an integrated IMS infrastructure, as described above, one has to be aware of certain assignment issues. If subscriber B (RCS-message-only) is registered in the S-CSCF of an integrated IMS infrastructure and subscriber A is also registered with the same IMS infrastructure, then subscriber A may try to invite subscriber B to a voice session, e.g. VoLTE/VoWiFi. The S-CSCF of the IMS would try to terminate this voice session towards UE B, by passing a related invitation message to UE B, because it is unaware of the capabilities of UE B (or more precisely because it cannot do SIP session termination or rerouting to CS network based on the UE's capabilities). As subscriber B is not capable of/authenticated for VoLTE/VoWiFi the termination would fail. Hence, there is a source for erroneous invitation requests in common integrated IMS infrastructures. Thereby, it does not matter, if subscriber B is connected to a different IMS infrastructure than subscriber A. In case subscriber A and subscriber B are registered within one IMS infrastructure, the connection is established within said one infrastructure. In case subscriber B is registered in another IMS infrastructure, an I-CSCF may establish a connection to an S-CSCF of a remote IMS infrastructure. Hence, in any case connections to subscribers in the same or in different networks can be established.
Hence, it is an objective of the present invention to solve or alleviate the technical problems and disadvantages set forth above. Hereunto, the present invention describes an integrated IMS infrastructure for different IMS services, respectively IM service and VoLTE/VoWiFi service, wherein user assignment and session termination is unambiguous and fail-safe.